Method for fabricating and transporting an integrated buoyancy system

ABSTRACT

A buoyancy system includes a plurality of buoyancy joints distributed along a riser system. Each joint can include a riser pipe, an external frame disposed around a riser and a vessel, and a buoyant cladding disposed between the vessel and the frame.

This is a divisional of U.S. patent application Ser. No. 10/918,048,filed Aug. 12, 2004, which claims priority of U.S. Provisional PatentApplication Nos. 60/568,101, filed May 3, 2004, and 60/568,478, filedMay 5, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to buoyancy for offshore oilproduction.

2. Related Art

As the cost of oil increases and/or the supply of readily accessible oilreserves are depleted, less productive or more distant oil reserves aretargeted, and oil producers are pushed to greater extremes to extractoil from less productive oil reserves, or to reach more distant oilreserves. Such distant oil reserves may be located below the oceans, andoil producers have developed offshore drilling platforms in an effort toextend their reach to these oil reserves. In addition, some oil reservesare located farther offshore, and thousands of feet below the surface ofthe oceans.

For example, vast oil reservoirs have recently been discovered in verydeep waters around the world, principally in the Gulf of Mexico, Braziland West Africa. Water depths for these discoveries range from 1500 tonearly 10,000 ft. Conventional offshore oil production methods using afixed truss type platform are not suitable for these water depths. Theseplatforms become dynamically active (flexible) in these water depths.Stiffening them to avoid excessive and damaging dynamic responses towave forces is prohibitively expensive.

Deep-water oil and gas production has thus turned to new technologiesbased on floating production systems. These systems come in severalforms, but all of them rely on buoyancy for support and some form of amooring system for lateral restraint against the environmental forces ofwind, waves and current.

These floating production systems (FPS) sometimes are used for drillingas well as production. They are also sometimes used for storing oil foroffloading to a tanker. This is most common in Brazil and West Africa,but not in Gulf of Mexico as of yet. In the Gulf of Mexico, oil and gasare exported through pipelines to shore.

Certain floating oil platforms, i.e., Spars or Deep Draft CaissonVessels (DDCV), and large “Semi-submersibles” have been developed toreach these deep-water oil reserves. Most of these floating platformsare designed to maximize the platform's ability to produce and processcrude oil (thus maximizing revenue), while at the same time minimize theoverall size and mass of the platform hull and thus minimize therequired capital investment. For this reason, it is advantageous toutilize the available hull buoyancy for topside processing equipment,and to minimize or even decouple other “parasitic” weight that wouldotherwise increase capital costs or reduce revenue-generating payload.

Steel tubes or pipes, known as risers, are suspended from these floatingplatforms, and extend the thousands of feet to reach the ocean floor,and the oil reserves beyond.

Typical risers are either vertical (or nearly vertical) pipes held up atthe surface by tensioning devices (called Top Tensioned riser); orflexible pipes which are supported at the top and formed in a modifiedcatenary shape to the sea bed; or steel pipe which is also supported atthe top and configured in a catenary to the sea bed (Steel CatenaryRisers—commonly known as SCRs).

The flexible and SCR type risers may in most cases be directly attachedto the floating vessel. Their catenary shapes allow them to comply withthe motions of the FPS caused by environmental forces. These motions canbe as much as 10-20% of the water depth horizontally, and 10 s of feetvertically, depending on the type of vessel, mooring and location.

Top Tensioned Risers (TTRs) typically need to have higher tensions thanthe flexible risers, and the vertical motions of the vessel need to beisolated from the risers. TTRs have significant advantages forproduction over the other forms of risers, however, because they allowthe wells to be drilled directly from the FPS, avoiding an expensiveseparate floating drilling rig. Also, wellhead control valves placed onboard the FPS allow for the wells to be maintained from the FPS.Flexible and SCR type production risers require the wellhead controlvalves to be placed on the seabed where access is difficult andmaintenance is expensive. These surface wellhead and subsurface wellheadsystems are commonly referred to as “Dry Tree” and “Wet Tree” types ofproduction systems, respectively. Drilling risers must be of the TTRtype to allow for drill pipe rotation within the riser. Export risersmay be of either type.

TTR tensioning systems are a technical challenge, especially in verydeep water where the required top tensions can be 1,000,000 lbs (1,000kips) or more. Some types of FPS vessels, e.g. ship shaped hulls, haveextreme motions which are too large for TTRs. These types of vessels areonly suitable for flexible risers, or other free-standing systems.Other, low heave (vertical motion), FPS designs are suitable for TTRs.This includes Tension Leg Platforms (TLP), Semi-submersibles and Spars,all of which are in service today.

One type of riser tensioning system that may be employed calls forbuoyancy that is distributed along the vertical length of the riser.Depending on the total weight of each riser (which determines how muchnet buoyancy is desired) and other requirements, it may be moreadvantageous to attach buoyant elements along the entire length of theriser system, rather than to concentrate all the buoyancy near thesystem's upper end.

Of the aforementioned floating production systems, only the TLP and Sparplatforms use TTR production risers. Semi-submersibles may use TTRs fordrilling risers, but these must be disconnected in extreme weather.Production risers need to be designed to remain connected to the seabedin extreme events, typically the 100 year return period storm. Only verystable vessels, such as TLPs and Spars are suitable for this.

Early TTR designs employed on semi-submersibles and TLPs used activehydraulic tensioners to support the risers by keeping the tensionrelatively constant during wave motions. As tensions and strokerequirements grow, these active tensioners become prohibitivelyexpensive. They also require large deck area, and the buoyancy loadshave to be carried by the FPS structure.

Spar type platforms recently used in the Gulf of Mexico use a passivemeans for tensioning the risers. These type platforms have a very deepdraft with a central shaft, or centerwell, through which the riserspass. Types of spars include the Caisson Spar (cylindrical), the “Truss”spar and “Cell” spar. There may be as many as 40 production riserspassing through a single centerwell. Even the most recent designs forlarge buoyancy cans used on Spars are limited in diameter and overalllength, and may not be feasible or cost-effective where the net buoyancyrequirement is in the range of 3000-4000 kips. This may be driven by theneed to employ very heavy wall, or double wall riser pipe systems. Incases such as this, it may be more cost-effective to utilize a system ofdistributed buoyancy elements, rather than conventional air cans used onTTRs.

The underlying principal of both TTR buoyancy cans and distributedbuoyancy systems is to remove a load-bearing connection between thefloating vessel and the risers. Whether located at the top of the risersystem (near the water surface) or distributed along the riser's totallength, the buoyant elements need to provide enough buoyancy to supportthe required tension in the risers, the weight of the buoyant elements,and the weight of the surface wellhead. One disadvantage with TTR aircans is that they are normally formed of metal, and thus addconsiderable weight themselves. Thus, the metal air cans must supportthe weight of the risers and themselves. In addition, the air cans areoften built to pressure vessel specifications, and are thus costly andtime consuming to manufacture.

Conventional designs for distributed buoyancy systems are based onfoam-filled, half-round sections that are mechanically attached (bolted)around a riser pipe. Storage and staging of these buoyancy sections canbe a cumbersome task on an offshore platform, where open deck space isall but nonexistent. Installation is likewise time-consuming andrequires heavy tools.

As risers have become longer by going deeper, their weight has increasedsubstantially. One solution to this problem has been to simply increasethe number of buoyant sections added to each riser string, since themaximum diameter of said buoyant shells is normally limited to thatwhich will pass through the rotary table while the riser joints arebeing “run,” or assembled and lowered into the water.

One problem with typical buoyancy systems is that if they are toptensioned, and the buoyancy force is concentrated at the top of theriser, it may result in higher stress, strain and/or forceconcentrations. Another problem with buoyancy is water pressure,especially at greater depths, that can crush conventional buoyancy cansor the like. While some buoyancy systems resolve that problem byutilizing expensive, crush-resistant foams, the foams themselves areusually very dense and can be very expensive. Yet another problem withproviding buoyancy is transportation of the buoyancy system to the drillsite, or the offshore platform. A related problem is the expense anddifficulty of installing and/or assembling the buoyancy system. Manysystems can be labor intensive and inefficient to install.

SUMMARY OF THE INVENTION

It has been recognized that it would be advantageous to develop animproved buoyancy system for offshore oil platforms. It has beenrecognized that it would be advantageous to develop a buoyancy systemthat is inexpensive and easy to manufacture, transport, and install. Ithas been recognized that it would be advantageous to develop a buoyancysystem that can be distributed along the length of the riser, whileresisting crushing by water pressure.

The invention provides a buoyancy joint configured to provide buoyancyfor a riser system of an offshore platform. The buoyancy joint includesa vessel coupled to a riser section and pressurized with gas. Anexternal frame is disposed around the vessel, and an enclosuresubstantially encloses the vessel and defines a space between theenclosure and the vessel. A buoyant cladding is disposed in the spacebetween the vessel and the enclosure.

In accordance with one aspect of the present invention, the enclosurecan include a plurality of flat panels forming a rectilinear box.

In accordance with another aspect of the present invention, a pluralityof buoyancy joints can have a transportation configuration and anoperational configuration. In the transportation configuration, theplurality of buoyancy joints is bundled together. In the operationalconfiguration, the plurality of buoyancy joints is coupled along a risersystem.

The invention provides a method for transporting and installing buoyancyfor a riser of an offshore platform. The method includes providing aplurality of buoyancy joints, each buoyancy joint having an externalframe with a lateral perimeter having at least three linear sides. Theplurality of buoyancy joints is bundled together in a bundledconfiguration with the buoyancy joints laterally adjacent one anotherand the linear sides of adjacent buoyancy joints abutting one another.The plurality of buoyancy joints is transported in the bundledconfiguration from a manufacturing site to a field site. The pluralityof buoyancy joints is disposed along a riser system extending submergedbetween the offshore platform and a wellhead with riser sections of thebuoyancy joints operatively coupled in series and in fluid communicationwith riser sections of the riser system.

The invention provides a method for fabricating a buoyancy joint for ariser of an offshore platform. The method includes providing a vesselwith opposite apertures at opposite longitudinal ends capable ofreceiving a riser section therethrough, and an enclosure formedsubstantially around the vessel. Foam is injected into the enclosure tosubstantially fill space between the vessel and the enclosure.

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of an integrated buoyancy joint(IBJ) of a buoyancy system in accordance with an embodiment of thepresent invention;

FIG. 2 is a cross-sectional end view of the integrated buoyancy joint ofFIG. 1;

FIG. 3 is a schematic side view of an offshore platform with a risersystem and a buoyancy system including a plurality of integratedbuoyancy joints of FIG. 1;

FIG. 4 is a perspective view of a plurality of integrated buoyancyjoints of a buoyancy system of FIG. 1 shown in a horizontaltransportation configuration;

FIG. 5 is a perspective view of a plurality of integrated buoyancyjoints of a buoyancy system of FIG. 1 shown in a vertical transportationconfiguration;

FIG. 6 is a partial side view of the integrated buoyancy joint of FIG.1; and

FIG. 7 is a partial end view of the integrated buoyancy joint of FIG. 1.

DETAILED DESCRIPTION

Reference will now be made to the exemplary embodiments illustrated inthe drawings, and specific language will be used herein to describe thesame. It will nevertheless be understood that no limitation of the scopeof the invention is thereby intended. Alterations and furthermodifications of the inventive features illustrated herein, andadditional applications of the principles of the inventions asillustrated herein, which would occur to one skilled in the relevant artand having possession of this disclosure, are to be considered withinthe scope of the invention.

As illustrated in FIGS. 1-7, a buoyancy system, indicated generally at10, in accordance with the present invention is shown for providingbuoyancy to a riser system 14 extending from an offshore oil platform 18to wellheads or control modules on the ocean floor. The system 10 caninclude a plurality of integrated buoyancy joints (IBJ) 22 that can becoupled in series with a plurality of riser sections 26 along the lengthof the riser system in an operational configuration, as shown in FIG. 3.Buoyancy elements are permanently affixed to individual riser sections,or “joints,” forming integrated modules that are then distributedperiodically along the length of the riser system 14. The riser system14 can include a plurality of individual, discrete riser sections 26coupled together in series to form a continuous riser system. The risersections 26 can include elongated pipes with hollows therein to conveyoil, gas or the like from the wellhead to the oil platform.

Deep water oil drilling and production is one example of a field thatmay benefit from use of such a buoyancy system 10. The term “deep water,floating oil platform” is used broadly herein to refer to buoyantplatforms located above and below the surface, such as are utilized indrilling and/or production of fuels, such as oil and gas, typicallylocated off-shore in the ocean at locations corresponding to depths ofover several hundred or thousand feet, including classic, truss, andconcrete spar-type platforms or Deep Draft Caisson Vessels, etc. Thus,the fuel, oil or gas reserves are located below the ocean floor atdepths of over several hundred or thousand feet of water.

A truss-type, floating platform 18 is shown schematically in FIG. 3, andhas above-water, or topside, structure, and below-water, or submerged,structure. The above-water structure includes several decks or levelswhich support operations such as drilling, production, etc., and thusmay include associated equipment, such as a work over or drilling rig,production equipment, personnel support, etc. The submerged structuremay include a hull, which may be a full cylinder form. The hull mayinclude bulkheads, decks or levels, fixed and variable seawaterballasts, tanks, etc. The fuel, oil or gas may be stored in tanks in thehull. The platform, or hull, also has mooring fairleads to which mooringlines, such as chains or wires, are coupled to secure the platform orhull to an anchor in the sea floor.

The hull also may include a truss or structure. The hull and/or trussmay extend several hundred feet below the surface of the water, such as600 feet deep. A centerwell or moonpool is located in the hull or trussstructure. One or more riser systems or lengths of riser pipe extendthrough the hull, truss, and/or centerwell. The centerwell is typicallyflooded and contains compartments or sections for separating the risers.The hull provides buoyancy for the platform 18 while the centerwellprotects the risers.

It is of course understood that the truss-type, floating platform 18depicted in FIG. 3 is merely exemplary of the types of floatingplatforms that may be utilized. For example, other spar-type platformsmay be used, such as classic spars, or concrete spars.

The risers or riser systems 14 are typically steel pipes or tubes with ahollow interior for conveying the fuel, oil or gas from the reservoir,to the floating platform 18. The pipes or tubes extend between thereservoir and the floating platform 18, and include production risers,drilling risers, and export/import risers. The riser system may extendto a surface platform or a submerged platform. The riser systems 14 canbe coupled to the platform 18 by a thrust plate located on the platform18 such that the riser systems 14 are suspended from the thrust plate.The buoyancy system 10 can support deep water risers or deep water risersystems. The term “deep water risers” or “deep water riser system” isused broadly herein to refer to pipes or tubes extending over severalhundred or thousand feet between the reservoir and the floating platform18, including production risers, drilling risers, and export/importrisers.

In one aspect, the buoyancy system 10 is utilized to access deep-wateroil and gas reserves with deep-water riser systems 14 which extend toextreme depths, such as over 1000 feet, over 3000 feet in anotheraspect, and over 5000 feet in yet another aspect. It will be appreciatedthat thousand feet lengths of steel pipe are exceptionally heavy, orhave substantial weight. It also will be appreciated that steel pipe isthick or dense (i.e. approximately 0.283 lbs/in³), and thus experiencesrelatively little change in weight when submerged in water, or seawater(i.e. approximately 0.037 lbs/in³). Thus, for example, steel onlyexperiences approximately a 13% decrease in weight when submerged.Therefore, thousands of feet of riser, or steel pipe, is essentially asheavy, even when submerged.

The buoyancy system 10 can be coupled to or along the riser systems 14to support or provide buoyancy to the riser systems. The buoyancy system10 includes one or more integrated buoyancy joints (IBJs) 22 which aresubmerged and filled with a buoyant material, such as air, to produce abuoyancy force to buoy or support the riser systems 14.

As stated above, the thousands of feet of risers exert a substantialdownward force on the buoyancy system 10. It will be appreciated thatthe deeper the targeted reservoir, or as drilling and/or productionmoves from hundreds of feet to several thousands of feet, the riserswill become exceedingly more heavy, and more and more buoyancy forcewill be required to support the riser systems. In addition, it will beappreciated that deeper depths exert extremely high pressures.Furthermore, it will be appreciated that deeper depths are often foundfurther from shore, or from manufacturing sites, making transportationof equipment an issue. It has been recognized that it would beadvantageous to improve the systems and processes for accessing deepreserves, improve the manufacture and transportation of buoyancy forriser systems to reduce the weight of the risers and platforms, andincrease the buoyant force.

Referring to FIGS. 1 and 2, each integrated buoyancy joint 22 caninclude an elongated riser section 30. The riser section 30 can be a 12″steel production riser pipe with a length of approximately 20-60 feet.As described above, the riser section 30 of the buoyancy joint 22 can becoupled in series with riser section 26 of the riser system 14 to form acontinuous hollow tube for transporting fuel, oil, gas or the like.

A vessel 34 is coupled to and laterally surrounds the riser section 30.The vessel 34 can include a pair of hemispherical domes 38 separated by,and joint to, an intermediate section or tube 44. Each dome 38 can havean aperture through which the riser section 30 extends. Thus, the risersection 30 can extend through a center of the vessel 34, the domes 38and the intermediate section or tube 44, and can define a longitudinalaxis of the buoyancy joint 22. The domes 38 can be sealed around theriser section 30, and to the intermediate section or tube 44, to formthe vessel 34, and an enclosure with or around the riser section. A seal48 can be disposed between the domes 38 and the riser section 30. Thevessel 34 can be filled with a buoyant material, such as air, or anothergas, such as nitrogen. In addition, the vessel 34 can be pressurized toresist pressure forces at great depths. The domes and intermediatesection or tube can be formed of fiber reinforced plastic, and can beoverwrapped with fiber or other structural material. Thus, the vessel 34can be lightweight to reduce the weight of the riser system 14, andstrong to resist internal and external pressures. Alternatively, thedomes and intermediate section can be formed of metal, such as steel.The vessel, or the domes and the intermediate section, can have adiameter of approximately 60 inches.

An external frame 52 can surround the vessel 34, and can laterallysurround the riser section 30. The frame 52 can form a rigid, externalskeleton or framework, and can include a plurality of interconnectedframe members. The frame 52 or frame members can be formed of metal,such as angle iron or tubes, welded together. The frame 52 can include apair of opposite end caps 56. The end caps 56 can form a lateralperimeter or outermost circumference of the buoyancy joint 22. The endcaps 56 can be shaped, or can have a cross-sectional shape with respectto the longitudinal axis, with at least three straight or linear sides.Thus, the shape of the end caps 56 can be triangular, rectangular,square, pentagonal, hexagonal, octagonal, etc. The straight or linearportions of the perimeter or circumference of the frame facilitatestacking, storage and transportation of the buoyancy joints 22, asdiscussed in greater detail below.

The end caps 56 can include apertures 58, eyes, or similar devices tofacilitate lifting, such as being engaged by hooks. The frame 52 canalso include longitudinal members 60 interconnecting the end caps 56,and lateral members 62 interconnecting the longitudinal members 60. Thelongitudinal members can extend along the edges of the buoyancy joints.The end caps 56 can include perimeter members 64 and radial members 66extending between the riser section 30 and the perimeter members 64.

The external frame 52 or members thereof can be formed of metal, such assteel, welded or bolted together. For example, angle iron can be used tofabricate the frame. Alternatively, non-metallic or hybrid material canbe used.

An enclosure 70 is associated with the external frame 52, andsubstantially encloses the vessel 34. A space is defined between theenclosure 70 and the vessel 34. The frame 52 can extend around theenclosure 70, such as at the edges. The enclosure 70 can include aplurality of flat panels 74 forming a rectilinear box. The flat panels74 can be formed by fiber reinforced plastic. Again, the fiberreinforced plastic can reduce weight of the buoyancy system 10 or risersystem 14. Alternatively, the flat panels can be formed of metal, suchas steel. The enclosure 70 or flat panels 74 can be carried by, orsupported by, the frame 52. Alternatively, the enclosure or flat panelscan extend around an exterior of the frame.

A buoyant cladding 80 is disposed in the space between the vessel 34 andthe external frame 52. The cladding 80 can be buoyant to provideadditional buoyancy, and can be rigid to provide structural rigidity toresist pressure forces. For example, the cladding 80 can be formed of,or can include foam or syntactic foam.

The vessel 34 can have an outer diameter that substantially equals aninner diameter of the enclosure 70, as shown in FIG. 2, so that thevessel maximizes a volume defined by the enclosure 70, and minimizes thespace between the vessel and the enclosure. The vessel 34 can occupy amajority of the space within the frame or enclosure, thus reducing theamount of syntactic foam used. The vessel can be pressurized withinexpensive buoyant material, such as air or nitrogen. The pressurizedvessel and syntactic foam cladding provide crush resistance at greatdepths. Thus, the buoyancy joint can maximize use of less expensivebuoyancy, such as compressed air or nitrogen, while minimizing the useof more expensive buoyancy, such as syntactic foam. The cladding 80 canbe formed in any number of sections, disposed around the vessel. Inaddition, the cladding can have an internal cavity with a circularcross-section and a hemispherical shape to match the domes andintermediate section of the vessel. The cladding can have an outerrectilinear shape to match the rectilinear shape of the frame orenclosure. Therefore, the space within the buoyancy joint is efficientlyused for buoyancy.

The buoyancy system 10 or plurality of integrated buoyancy joints 22 canhave an operational configuration, as shown in FIG. 3, and atransportation configuration, as shown in FIGS. 4 or 5. In the operationconfiguration, the plurality of buoyancy joints 22 are coupled along thelength of the riser system 14, and can form a continuous conduit withthe other riser sections. In the transportation configuration, thebuoyancy joints 22 can be stacked and/or bundled together. The buoyancyjoints 22 can be oriented horizontally during transportation, as shownin FIG. 4, such as on a barge or deck boat 100. Alternatively, thebuoyancy joints 22 can be oriented vertically during transportation, asshown in FIG. 5. Thus, the buoyancy joints 22 can be safely andconveniently transported to the oil platform for use. As describedabove, the end caps 56, or sides thereof, can abut to and stack with theend caps of adjacent buoyancy joints. The straight or rectilinear sidesof the buoyancy joints facilitate stacking and transportation.

Referring to FIGS. 6 and 7, a pressurization tube 110 or pressure portcan extend to the vessel 34 to allow a pressurized gas to be introducedinto the vessel. The pressurization tube 110 or pressure port can bepositioned on a side of the buoyancy joint 22, and can extend throughthe enclosure 70 or panels 74, through the cladding 80, and through thevessel 34. Alternatively, the pressurization tube 110 or pressure portcan extend through the seal between the dome and the riser. Thepressurization tube or pressure port is an example of one means forpressurizing the vessel. The pressurization tube or pressure port can beaccessible by a submersible ROV (remotely operated vehicle) so that thevessel can be pressurized while under water, even at great depth.

As indicated above, in operation, the buoyancy joints 22 can bespaced-apart or distributed along the length of the riser system 14.Thus, the buoyancy system can provide a distributed buoyancy force alongthe length of the riser. The buoyancy joints can be separated by risersections 26. For example, the buoyancy system, or modules thereof, canbe configured to provide thousands of kips net buoyancy along a 10,000foot riser. The buoyancy system can provide the primary buoyancy for theriser, or an auxiliary (supplemental) buoyancy. Thus, the individualbuoyancy joints are sized to produce at least 50 kips net buoyancy. Thevessels and shrouds of each module can be sized and shaped to provide adesired buoyancy force at a designated depth. Thus, the vessels can havedifferent lengths and/or diameters with respect to one another.

The modules or frames can include trim tabs, boards, or helical strakesto offset vortex-induced vibration (VIV), and reduce drag due to movingcurrent in the water. Module frames that are triangular in cross-sectionmay also improve VIV or reduce drag from underwater currents.

The IBJ modules can be fabricated on shore, stacked, and shipped to thefloating oil platform, where they can be installed. The rectilinearframes facilitates stacking and transportation. The vessels can bepressurized (as dictated by service depth) during installation, orafter.

The riser section 30 of the buoyancy joint can be provided “bare,” orcan be a continuous tube or pipe. Alternatively, the riser section 30can be provided with a standard or custom coupling 130 (top and/orbottom). The coupling 130 can be an enlarged pipe to receive the ends ofthe riser section 30 therein, and secured by welding.

The external frame and/or integrated buoyancy joint can be shaped tofacilitate transportation, stacking and storage. For example, the framecan have a rectilinear shape. In addition, the frame or integratedbuoyancy joint can have a shape to efficiently utilize space or maximizebuoyancy within given restraints. It will be appreciated that theintegrated buoyancy joints may be disposed in, or may pass through,centerwells or rotary tables with cross-sectional openings therein.Thus, the shape of the integrated buoyancy joint or frames can maximizethe buoyancy while still passing through the openings.

A method for transporting and installing buoyancy for a riser system 14of an offshore platform 18 includes providing a plurality of buoyancyjoints 22 as described above, each having an external frame 52 with alateral perimeter having at least three linear sides. The plurality ofbuoyancy joints are bundled together in a bundled configuration, asshown in FIGS. 4 and 5, with the buoyancy joints laterally adjacent oneanother and the linear sides of adjacent buoyancy joints abutting oneanother. The plurality of buoyancy joints are transported in the bundledconfiguration from a manufacturing site to a field site. The pluralityof buoyancy joints are disposed along the riser system 14 extendingsubmerged between the offshore platform and a wellhead. The risersections of the buoyancy joints are operatively coupled in series and influid communication with riser sections of the riser system.

As shown in FIG. 4, the plurality of buoyancy joints 22 can be disposedin a stacked configuration with each buoyancy joint in a horizontalorientation. In addition, the plurality of buoyancy joints in thebundled configuration on a deck of a barge or a deck boat, as shown.

The buoyancy joints can be lifted and manipulated by engaging lift-eyes58 in the external frames of the buoyancy joints with hooks. Forexample, the buoyancy joints can be lifted onto the platform, andpositioned for coupling along the riser system.

A method for fabricating a buoyancy joint for a riser of an offshoreplatform described above can include providing a vessel with oppositeapertures at opposite longitudinal ends and capable of receiving a risersection therethrough, and an enclosure formed substantially around thevessel. Foam can be injected into the enclosure to substantially fillspace between the vessel and the enclosure, and form the buoyancycladding.

It is to be understood that the above-referenced arrangements are onlyillustrative of the application for the principles of the presentinvention. Numerous modifications and alternative arrangements can bedevised without departing from the spirit and scope of the presentinvention. While the present invention has been shown in the drawingsand fully described above with particularity and detail in connectionwith what is presently deemed to be the most practical and preferredembodiment(s) of the invention, it will be apparent to those of ordinaryskill in the art that numerous modifications can be made withoutdeparting from the principles and concepts of the invention as set forthherein.

1. A method for transporting and installing buoyancy for a riser of anoffshore platform, comprising the steps of: a) providing a plurality ofbuoyancy joints, each buoyancy joint having an external frame with alateral perimeter having at least three linear sides; b) bundling theplurality of buoyancy joints together in a bundled configuration withthe buoyancy joints laterally adjacent one another and the linear sidesof adjacent buoyancy joints abutting one another; c) transporting theplurality of buoyancy joints in the bundled configuration from amanufacturing site to a field site; and d) disposing the plurality ofbuoyancy joints along a riser system extending submerged between theoffshore platform and a wellhead with riser sections of the buoyancyjoints operatively coupled in series and in fluid communication withriser sections of the riser system.
 2. A method in accordance with claim1, wherein the step of bundling further includes the step of: stackingthe plurality of buoyancy joints in a stacked configuration with eachbuoyancy joint in a horizontal orientation.
 3. A method in accordancewith claim 1, wherein the step of transporting further includes the stepof: disposing the plurality of buoyancy joints in the bundledconfiguration on a deck of a barge or a deck boat.
 4. A method inaccordance with claim 1, wherein the step of disposing further includesthe step of: engaging lift-eyes in the external frames of the buoyancyjoints with hooks; lifting the buoyancy joints with the hooks; andpositioning the buoyancy joints for coupling along the riser system. 5.A method in accordance with claim 1, wherein the step of providing aplurality of buoyancy joints, further comprises providing a plurality ofbuoyancy joints each comprising: a) a riser section; b) a vessel,directly coupled to the riser section, configured to be pressurized withgas; c) the external frame disposed around the vessel; d) an enclosure,associated with the external frame and substantially enclosing thevessel, defining a space between the enclosure and the vessel; and e) abuoyant cladding, disposed in the space between the vessel and theenclosure.
 6. A method in accordance with claim 5, wherein the enclosureincludes a plurality of flat panels forming a rectilinear box.
 7. Amethod in accordance with claim 6, wherein the flat panels include fiberreinforced plastic.
 8. A method in accordance with claim 5, wherein eachof the plurality of buoyancy joints has a vessel with a diameter orlength that is different from respective diameters or lengths of vesselsof other buoyancy joints associated with the riser system.
 9. A methodin accordance with claim 5, wherein the enclosure forms a moldconfigured to receive an uncured foam material therein to form thebuoyant cladding.
 10. A method in accordance with claim 5, wherein: thevessel includes a fiber reinforced plastic; the buoyant claddingincludes rigid foam; and the enclosure includes a fiber reinforcedplastic.
 11. A method in accordance with claim 5, wherein the buoyantcladding includes rigid foam substantially filling the space between thevessel and the enclosure.
 12. A method in accordance with claim 5,wherein the vessel fills a majority of a volume defined by the externalframe, and the cladding fills a minority of the volume with respect tothe vessel.
 13. A method in accordance with claim 5, wherein the vesselhas an outer diameter that substantially equals an inner diameter of theenclosure.
 14. A method in accordance with claim 5, wherein thecross-sectional shape is selected from the group consisting of: square,rectangular, triangular, pentagonal, hexagonal, and octagonal.
 15. Amethod in accordance with claim 5, wherein the vessel has asubstantially circular cross-sectional shape with respect to thelongitudinal axis.
 16. A method in accordance with claim 5, wherein thevessel includes opposite, spaced-apart, hemispherical domes, each havingan aperture through which the riser section extends, and seals formedbetween the riser section and the domes.
 17. A method in accordance withclaim 5, wherein the external frame includes: a pair of spaced apart endcaps having an outer perimeter orthogonal to a longitudinal axis shapedwith at least three linear sides; longitudinal members, extendingbetween the end caps; and lateral members, extending between the risersection and the outer perimeter.
 18. A method in accordance with claim5, wherein the external frame includes: means for intercoupling theexternal frame with other external frames of other buoyancy jointsbundled together.
 19. A method in accordance with claim 5, furthercomprising means for joining the riser section to other riser sections.20. A method in accordance with claim 5, further comprising apressurization tube extending into the vessel for pressuring the vessel.21. A method for fabricating a buoyancy joint for a riser of an offshoreplatform, comprising the steps of: a) providing a vessel with oppositeapertures at opposite longitudinal ends capable of receiving a risersection therethrough, and an enclosure formed substantially around thevessel; and b) injecting foam into the enclosure to substantially fillspace between the vessel and the enclosure.
 22. A method in accordancewith claim 21, wherein step a) further includes the steps of: a)disposing the vessel about the riser section and forming a frame aroundthe vessel; and b) forming the enclosure around the vessel.
 23. A methodin accordance with claim 21, further comprising the step of: forming thevessel with a fiber reinforced plastic and overwrapping the vessel withfiber reinforcement.